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Old 20th Jul 2018, 11:27 am   #1
regentone001
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Default Regentone Ten-17

hi guys
this set has worked well for the past 18 months being in regular use. It has been recapped. The other day it was working ok and had been on for a couple of hours when it started to develop sound on vision, this got rapidly worse. I can almost get rid of it with the contrast control then I lose sync, the fine tuner doesn't get rid of it in fact it gets worse and if turned in one direction the sound becomes weak and very distorted.
Anyone any ideas where to start to check? Could it be the agc?
Thanks
Steve
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Old 20th Jul 2018, 4:45 pm   #2
FERNSEH
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Default Re: Regentone Ten-17

First of all avoid touching the cores of the IF transformers, do not twiddle!
As the vision AGC is derived from the DC restoring properties of the sync separator that should the first part of the receiver to check. There might be a possibility that the AGC to the tuner is missing or diminished by a leaky decoupling capacitor.

DFWB.
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Old 20th Jul 2018, 9:21 pm   #3
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Default Re: Regentone Ten-17

Very possible David but I wonder if the anode load of the local oscillator has risen in value.
It creates odd symptoms. J.
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Old 21st Jul 2018, 1:54 am   #4
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Default Re: Regentone Ten-17

Hi John,
That's a good tip. The oscillator resistor consists of R10A and R10B in series. 4.7Kohms and 6-8Kohms 2watt.
Cyldon type "C" turret tuner.
Information for the Regentone Ten-17 can be found in the 1960/61 Radio and Television servicing book.

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Old 21st Jul 2018, 8:40 am   #5
regentone001
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Default Re: Regentone Ten-17

Hi Guys I found the culprit. R27 (as marked on circuit board) which supplies bias voltage to the cathode of V5P the pentode section of the PCF80 (video amp) had dropped in value from 27k to just over 9k. The voltage had risen from 4v to over 17v. I replaced it and was back to normal. I am surprised that it changed so suddenly as up until the other night the set has worked without any problems for over 18 months since I recapped it.
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Old 21st Jul 2018, 11:30 am   #6
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Default Re: Regentone Ten-17

The attached circuit diagram shows the circuit of the video amplifier.
The function of R27 is provide a degree of DC stabilising for the cathode bias of V5P.
When the resistor became low value the cathode bias rose to a level which caused clipping of the negative going sync pulses. This in turn caused the problems with the AGC and finally the loss of sync.


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